Used-hardware dealer customer and GPU appraisal registration

A scav-type seller visits now and then with three to five used cards. An
honest dealer sells at true value, a middleman adds 8%, a scammer mixes in
fakes (relabelled cheap chips) priced at 90% of the labelled model's value.
The markup is a client-temporary item feature, so a bought card is only
worth its real value. Cards are registered as appraisal items; the correct
value is the same function as the sale value.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Decentralized.Domain/UsedDealer.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Decentralized.Domain
+{
+    /// <summary>二手显卡贩子的类型：老实人按真实价卖；中间商加价；骗子夹带假卡，按标称型号的价卖。</summary>
+    public enum DealerKind { Honest, Middleman, Scammer }
+
+    /// <summary>贩子带来的一张卡：<see cref="MarkupPct"/> 是柜台上相对真实价值的加价百分比（骗子卖假卡时是正的，按标称型号报价再打九折）。</summary>
+    public sealed class UsedCard
+    {
+        public string Model;
+        public string FakeOf;
+        public double Health;
+        public int MarkupPct;
+    }
+
+    public static class UsedDealers
+    {
+        public const double MiddlemanMarkup = 0.08, ScamDiscount = 0.90;
+        public const double FakeShareMiddleman = 0.10, FakeShareScammer = 0.45;
+
+        /// <summary>今天来的贩子的类型：骗子越往后越多。</summary>
+        public static DealerKind Kind(int day, Rng rng)
+        {
+            double scam = Math.Min(0.30, 0.10 + day * 0.004);
+            double r = rng.NextDouble();
+            return r < scam ? DealerKind.Scammer : r < scam + 0.30 ? DealerKind.Middleman : DealerKind.Honest;
+        }
+
+        /// <summary>能出现在二手市场上的型号：按天数放开，旗舰第 30 天起。</summary>
+        public static string[] Pool(int day)
+        {
+            var list = new List<string>(Dealer.Basic);
+            if (day >= Dealer.AdvancedFromDay) list.AddRange(Dealer.Advanced);
+            if (day >= Dealer.FlagshipFromDay) list.AddRange(Dealer.Flagship);
+            return list.ToArray();
+        }
+
+        public static List<UsedCard> Cards(DealerKind kind, int day, Rng rng)
+        {
+            var pool = Pool(day);
+            int count = rng.Range(3, 5);
+            var cards = new List<UsedCard>();
+            for (int i = 0; i < count; i++)
+            {
+                double share = kind == DealerKind.Scammer ? FakeShareScammer : kind == DealerKind.Middleman ? FakeShareMiddleman : 0;
+                var label = pool[rng.Range(0, pool.Length - 1)];
+                var card = new UsedCard { Model = label, Health = 25 + rng.NextDouble() * 60 };
+                var cheaper = Hardware.Specs.Values.Where(s => !s.Asic && s.Price * 2 <= Hardware.Specs[label].Price).Select(s => s.Model).ToArray();
+                if (cheaper.Length > 0 && rng.Chance(share))
+                {
+                    card.FakeOf = cheaper[rng.Range(0, cheaper.Length - 1)];
+                    var u = new Unit { Model = card.Model, FakeOf = card.FakeOf, Health = card.Health };
+                    card.MarkupPct = (int)Math.Round((CardValue.Of(label, card.Health) * ScamDiscount / CardValue.True(u) - 1) * 100);
+                }
+                else if (kind == DealerKind.Middleman) card.MarkupPct = (int)Math.Round(MiddlemanMarkup * 100);
+                cards.Add(card);
+            }
+            return cards;
+        }
+    }
+}